Speaker
Description
Helping genetically unrelated others is seen across group-living species and may reflect social preferences including other-regard and inequality aversion. Whereas social preferences have been revealed in humans, there is ambiguous report on other-regard in non-human primates. Observed helping in non-human primates may reflect evolved social preferences but self-regard and by-product mutualism as alternative mechanisms cannot be excluded. Here, to examine whether and to what extent social preferences evolved in non-human primates, we performed social choice experiments in four different primate species—common marmosets, ruffed lemurs, ring-tailed lemurs, and mouse lemurs—that exhibit differences in social organization and care systems. Animals repeatedly chose between four options that gave a benefit (or not) to themselves and (or not) to a passive partner. The four options were regrouped into three orthogonal contrasts for self-regard, other-regard, and equality. Across our four primate species, we find significant positive self-regard, and no evidence for other-regard and inequality aversion (Experiment 1). The emergent social utility function reliably predicted choices in a helping task (Experiment 2). At the same time, for both self-regard and other-regard we find that animals living in less interdependent ecologies, like ruffed, ring-tailed, and mouse lemurs, display weaker self-regard and stronger other-regard compared to those living in more interdependent ecologies with clear role divisions between breeders and helpers (i.e., common marmosets). Results combined suggest weak support for other-regard and inequality aversion in non-human primates.
